1. Field of the Invention
The invention relates to electrochemical discharge machining, and more particularly to a feed control method for wire cutting electrochemical discharge machining and an apparatus thereof.
2. Description of the Related Art
Nonconductive brittle materials are widely used in micro-electro mechanical systems (MEMS) or biochips due their heat-resistant, deformation-resistant, and corrosion-resistant characters. However, if nonconductive brittle materials are processed using traditional machining methods, material removal rate may suddenly increase, such that machining precision is negatively influenced or the state of the machining operation may be uncontrollable due to fractured material surfaces. Thus, providing machining methods with high process feed speed and high precision is desired.
Generally, wire cutting and electrochemical discharge machining is not affected by strength and hardness of materials, so cutting of wires and machining with complicated paths and loci can be provided. For such a case, machining can be implemented using wire electrical discharge machining (WEDM) only if processed materials are conductible. However, nonconductive brittle materials cannot be processed using conventional wire electrical discharge machining methods. As such, combination of a wire electrical discharge machining method and an electrochemical discharge machining method has been disclosed.
Conventional electrochemical discharge machining methods at least comprise a weight weighting and feed method and a constant-speed feed machining method.
FIG. 1 is a schematic view of a weight weighting and feed method.
The weight weighting and feed method comprises a weight 110, being hung on an external process trough 120, so that gravity of the weight is imposed on an internal process trough 140 using the external process trough 120 and a slide rail mechanism 130, resulting in an automated feed operation. The automated feed forces a workpiece to carry a wire electrode for machining, such that there is no gap between the workpiece, in any position, and the wire electrode, which is a contact process. However, a rough workpiece surface may occur, since processes for only a portion of the contact workpiece is completed as un-processed workpieces are ignored to eliminate discharging by eliminating bubble generated at the contact point of the wire electrode and the processed workpiece. As described, drawbacks of the weight weighting and feed method comprise the rough surface and a slow process feed speed.
The constant-speed feed machining method allows a wire electrode or workpiece to be moved with a constant speed (a slower process feed speed) for machining. When the process feed speed is greater than an initial feed speed, the wire electrode does not contact with the workpiece so that a smooth surface can be obtained. Theoretically, if an optimum process feed speed can be provided, a smooth surface and a faster process feed speed can be obtained, but long-term monitoring and management are required. The process feed speed must be reduced once a contact event occurs, or a contact process will start to generate a rough surface and slow down the process feed speed, which might break the wire electrode. Thus, the constant-speed feed machining method is not appropriate to be used for automated machining.
Thus, a feed control method for wire cutting electrochemical discharge machining and an apparatus thereof are desirable. The method should improve the feed speed and prevent the wire electrode from contacting with the workpiece during machining, thereby achieving automated and complex machining and enhancing machining efficiency and precision.